\chapter*{Acknowledgements}
\textit{``Was du ererbt von deinen Vätern hast, erwirb es, um es zu besitzen.''}

Johann Wolfgang von Goethe
\vspace{1.5cm}

I would like to express my deepest gratitude to my supervisor, Prof.\ Dr.\ Gabriel Zachmann, for giving me the opportunity to carry out this thesis in an excellent research environment. I am especially grateful for the freedom he gave me to explore my own ideas, together with timely and constructive guidance whenever I needed it.


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